Radio tuning system



April 30, 1929. F. B. FALKNdR 1,710,753

RADIO TUNING SYSTEM Filed May 6, 1926 WITN SS S:v v IIQVENTOR Fran/1 B.Fa/lfnar w M BY ATTORNEY Patented Apr. 30, 1929.

UNITED STATES PATENT OFFICE.

FRANK FALKNOR, OF WILKINSBURG, PENNSYLVANIA, A SSI GNOR TO WESTING-HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA.

Application filed May 6,

My invention relates to systems used for the reception or amplificationof radio signals and it has particular reference to a tuning device usedfor either of these pur poses.

It has been very often noted when receiving radio signals, particularlythose at very high frequencies, that the frequency being received seemsto shift relatively slowly at irregular intervals.

This irregular shift in frequency is very detrimental, however, to goodreception, especially when use is made of the principle of regenerationto bring extremely weak signals up to good audibility. As is well known,regeneration increases the sharpness of tuning to a marked extent, andfor this reason, in receiving short wave signals on a regenerativesystem, the shift in frequency referred to above gives the effect offading.

The use of extremely high frequencies is becoming of increasingimportance both for long distance point-to-point comnmnication and forrelaying. When used for the latter purpose, it is of paramountimportance that none of the incoming signals be missed.

It is accordingly an object of my invention to provide a receivingsystem which will compensate for shifts in frequency of the transmittedsignals.

Another object of my invention is to construct a regenerative receiverthat shall in some respects operate as though it were broadly tuned.

A still further object of my invention is to devise means which may beintroduced into any tuned circuit of an amplifier to give the effect ofbroad tuning without introducing a damping factor.

A further object, broadly speaking, is to devise a radio receivingsystem which will, to some extent at least, offset the effect of fading.

In the preferred form of my invention, I attain these objects byprovidinga circuit which may be partially tuned to the exact frequencyat which the signal is expected to be received and, in addition to thearrange ments required for this preliminary tuning, I provide means forcontinually shifting the resonance point of the circuit over apredetermined range. My invention contemplates inserting in one of thecontrolling tuned circuits of the receiving system, a variable reactorsuch as a condenser or an inductor 1926. Serial No. 107,097.

and causing the value of this reactor to continuously and automaticallychange through a definite cycle.

This cycle is so chosen that the tuning of the circuit varies throughthe range of the shift in frequency which has been found byXpt'l'llllellt to prevail at the particular loca' tion of the receivingsystem.

The 'ate at which the tuning changes is adjusted until it is above thefrequency of the highest audio component of the incoming signal.

This variation in the tuning serves to broaden the resonance curve ofthe circuit thus equipped, or rather continually shifts the sharpresonance point over a narrow band of frequencies.

The circuit, while exhibiting some of the qualities of a damped circuit,is, at the same time sharply tuned to a. definite frequency at everyinstant, depending on the instantaneous value of the variable element.

I am thus enabled to get the effect of a broadly tuned circuit withoutthe disadvantages attcnding the use of damping means and the consequentloss of signal strength entailed thereby.

For a more complete understanding of my invention and the principlesunderlying its operation, reference is made to the drawing accompanyingthis specification and forming a part thereof, in which Fig. 1 is adiagrammatic view of a preferred form of my invention when employed witha regenerative receiver, while Fig. 2 is a similar view of amodification.

Referring now specifically to Fig. 1, a

complete single-tube regenerative receiver is indicated diagrammaticallyin order to more satisfactorily explain the operation and function ofthe system of my invention.

An antenna 1 is connected through an inductance 2 and a variablecondenser 3 to' ground 1. Coupled inductively to inductance 2, isanother inductance 5, shunted by a tuning condenser 6, and connectedatone side through a grid condenser 7 and agrid leak 8, to the grid 9,of a vacuum-tube device 10. The other side of this inductance 5, isconnected to the filament 11 of the tube 10 at the point 12. Connectedserially between the plate 13 and the filament 11, are a B battery 1s, apair of phones 15 shunted b a byass condenser 16, and a tickle-r oreed-bac inductance 17, which lat ter variably coupled to the inductance5. The tube 10 is provided with the usual A battery 18 and controlrheostat 19. The elements so far described are those customarilyincluded in the usual type of single-tube regenerati ve receiver.

Shunted across the input inductance 5 of the tube is an additionalcondenser 20, the movable element 21 oi which is {geared or otherwiseconnected to a motor 22 or to a analogous device. This motor is providedwith a stance of current 23, and arranged so that its speed may beadjusted. to any point desired.

When it is desired to receive a radio sit na on a. definite wave lei'u'th, the small variable condenser 20 first adjusted by hand to a pointwhere one halt of its total capacity is included in the circuit. Thecondenser 6 is nextadjusted until the circuit comprising inductance 5,condenser (3, condenser 20 and the 'apacity exist-h1g1 between gri d 9and filament 11, is tuned exactly to the incoming frequency. The antennaground circuit also tuned by means of the adjustable cendenser 3 and thecoupling between inductance 2 and inductance 5 is adjusted to that pointwhich gives the best selectivity. The coupling between the teed-backinductance 17 and the inductance 5 is also adjusted to the optimum pointand if necessary, the circuit as a whole is retuncd. This process oftuning is merely indicative of the steps usually involved in tuning aregenerative receiver.

Assuming now that the circuit is adjusted so as to receive the desiredsignals with the best audibility, a motor or other means 22 is startedand its speed is adjusted to vary the condenser 20 between its minimun'iand maximum capacity at a rate above audibility. The size oi thecondenser 20 is so chosen that its maximum capacity when introduced intothe circuit, serves to tune such circuit to resonance with the lowestfrequency to which the received signal varies, and when its capacity isa minimum, the circuit is then in resonance with the highest frequencyto which the incoming; signal shifts. The maximum value of thiscondenser 20 can only be determined by experiment, but in any event, itis comparatively low.

As stated above, the incoming signal tends to shift its :lrequeney atirregular intervals and it is obvious that it a circuit were constructed to tune broadly over the whole range oi frequency covered bythe incoming signal, none of the signals would be lost by reason 01these shifts. As is well known, however, in order to construct a circuitwhich tunes broadly, it is customary to introduce a damping :tactor.This damping causes losses and renders the system as a whole much lesssensitive to weak signals. 7

By means of my invention, however, I

l may he am enabled to shitt the tuning ot the circuit over the samerange of trcipiency through which the incoming sigi'ial passes, yet atthe same time, I introduce no additional damping means into the circuit.Inasmuch as this change in the tuning is preferably made at asuper-aiulible frequency, the re ception of. signals is not interferedwith. il anv iinatant, the ircuit is sharply tuned to a it linite 'lroipicncy and it only by reason oi the :tact that the successive tuningpoints elf the circuit extcn d over a frequency haml that the e'ltect ofbroad tuniitc is ohi ained.

lie'lerring j now specifically to Fig. 2, a circu t quite similar tothat oi. Fig. l. is diayiainniaticully shown. The only differencebetween the en nit shown in Fig. 2 and that shown in l ig. l is in thetype oi varialille reactor employed. instead of the variableco'i'uleimer El i shown in l.- ig. 1, I show a small variable imluctorfl-fl, in series with inductsr "1e 4") which imhictor is arranged tohave 1m value rontinually and rapidly varied.

The cll'ect of this variable inductor is cssentialiy the same as thougha cond ..er were used as in Fig. 1, but in some cases, it Bound thatsit-,nal strength, when employing the circuit of Fig. 2, is somewhatbetter than when employing the arrangement shown in Fl 1.

Although I have shown my invention as used in connection with asingletube regenerative receiver, it is not to be considered as limitedto such use. Either oi. the arrangements indicated may be employed withpractically any type of a receiver or amplifying circuit. F or instance,the resonant reeeipng circuit of a supe1.'-hetcrodyne sys tem might beequipped with my invention seu'iring substantially the same result. alsofeasible to apply my invention to the frequency control circuit of thegenerator used with a superlieterodyne receiver, or it might even beapplied to one of the intermediate circuits tuned to the beat frequency.These other applications of my invention are given merely by way ofexample as it is believed to be obvious that it may be applied topractically any tuned circuit involved in a receiver or amplifier whenthe signals to be received are subject to frequency shifts.

Among the principal :ulvantages result ing from the use of my inventionis that the reception of short-wave signals is very materially improved.It has been noted that, when a receiving system is equipped inaccordance with my invention such short-wave signals come through withsubstantially no fading whatever. This result is of very dccidedlyadvantage when these short wave signals are being used to control theoutput oi? a transmitter at a relay station, since it is obvious that inorder to secure perfect re- All transmission, none of the incomingsignals must be missed.

Another advantage lies in the reduction of distortion in the receivedsignals. The exact cause of this distortion is not definitely known butit is quite pronounced when ultra-high frequencies are being received.

Although I have illustrated and described herein certain specificembodiments of my invention, I am fully aware that many othermodifications are possible and my invention not to be limited except inso far as is necessitated by the prior art and as indicated by thefollowing claims.

I claim as my invention:

1. In a receiving device a circuit includ ing tuning means adapted to beadjusted to tune the circuit to any frequency within the range for whichthe receiving device is intended, and a continuouslv acting supplementaltuning device so disposed as to continuously and cyclically alter thefrequency said continuto which said circuit is tuned. ous alterationbeing a small fraction of the change said ad ust-able tuning means canproduce and being only as large as the maximum expected unintentionalvariation in the frequency to be received, the frequency of the cycle ofsaid continuous alteration being above audition.

2. The method of preventing loss of signals by a receiving set includinga tuned circuit comprising reactors of opposite sign through fadingcaused by frequency changes of said signals without increasing theresistance of said circuit, which consists in cyclically varying thereactance of the reactor of one sign, said variation having a periodabove audibility and an amplitude sufficient to include the frequencychanges which ordinarily cause fading and insuffi cient to cause loss ofsignal when the signal frequency is at its normal value, andsimultaneously producing an indication of said signals.

In testimony whereof, subscribed by name this 1926.

I have hereunto first day of May,

FRANK B. FALKNOR.

